1. Field of the Invention
The present invention relates to an intake control device for an engine for generating a tumbling flow of intake air in a cylinder.
2. Description of the Related Art
A conventional intake control device for an engine is disclosed in JP-A-2003-239751 (Patent Document 1) and JP-A-2003-278551 (Patent Document 2), for example. The intake control device for the engine disclosed in Patent Documents 1 and 2 includes a partition plate for partitioning an intake passage in an engine into an upper intake passage and a lower intake passage as seen along an axial direction of a crankshaft, and a tumble control valve provided in a vicinity of an upstream portion of the partition plate for opening or closing the lower intake passage.
The intake control device disclosed in Patent Document 1 includes a flow straightening member for regulating a flowing direction of intake air while being linked with the tumble control valve. The flow straightening member defines both side walls of a downstream end of the upper intake passage. The flow straightening member is in a position spaced from an intake valve in the upstream direction when the tumble control valve is open, and moves to a position adjacent to the intake valve when the tumble control valve is closed.
The flow straightening member approaches the intake valve, thereby intake air gathers in an area around the center of a combustion chamber, and thus a tumbling flow of the intake air is facilitated.
A function for changing a flowing direction of intake air for facilitating a tumbling flow as described above is achieved by the partition plate approaching toward the intake valve in the intake control device disclosed in Patent Document 2. The partition plate of the intake control device disclosed in Patent Document 2 is movably arranged in a cylinder head along the intake passage, and makes a parallel displacement linked with the opening or closing of the tumble control valve.
In the intake control devices disclosed in Patent Documents 1 and 2, when the tumble control valve is closed, intake air mainly flows in the upper intake passage. Consequently, in the intake control device, a flowing direction of intake air is regulated because of displacements of the flow straightening member and the partition plate toward the intake valve. As a result, in an engine including the intake control device disclosed in Patent Documents 1 and 2, a tumbling flow is generated in the cylinder because of intake air flowing from the upper intake passage into the cylinder. A tumbling flow means a whirling flow of intake air which is whirling around the center line extending in a direction intersecting with the axial line of the cylinder.
There is a limit to further generating an effective tumbling flow with the conventional intake control devices described above. It is believed that the limit occurs because when the tumble control valve is closed, drag of intake air becomes large and the flow coefficient largely decreases.
Also, the conventional intake control devices have to include a movable flow straightening member and a partition plate to facilitate a tumbling flow, and thus its construction is complicated.